Twentieth Century Delta δC Variability in Surface Water Dissolved Inorganic Carbon Recorded by Coralline Algae in the Northern North Pacific Ocean and the Bering Sea

The oxygen isotopic composition and Mg/Ca ratios in the skeletons of long-lived coralline algae record ambient seawater temperature over time. Similarly, the carbon isotopic composition in the skeletons record delta(13)C values of ambient seawater dissolved inorganic carbon. Here, we measured delta(13)C in the coralline alga Clathromorphum nereostratum to test the feasibility of reconstructing the intrusion of anthropogenic CO(2) into the northern North Pacific Ocean and Bering Sea. The delta(13)C was measured in the high Mgcalcite skeleton of three C. nereostratum specimens from two islands 500 km apart in the Aleutian archipelago. In the records spanning 1887 to 2003, the average decadal rate of decline in delta(13)C values increased from 0.03% yr(-1) in the 1960s to 0.095% yr(-1) in the 1990s, which was higher than expected due to solely the delta(13)C-Suess effect. Deeper water in this region exhibits higher concentrations of CO(2) and low delta(13)C values. Transport of deeper water into surface water (i.e., upwelling) increases when the Aleutian Low is intensified. We hypothesized that the acceleration of the delta(13)C decline may result from increased upwelling from the 1960s to 1990s, which in turn was driven by increased intensity of the Aleutian Low. Detrended delta(13)C records also varied on 4-7 year and bidecadal timescales supporting an atmospheric teleconnection of tropical climate patterns to the northern North Pacific Ocean and Bering Sea manifested as changes in upwelling.

New Pliocene and Pleistocene acritarchs from the North Atlantic, Arctic Ocean and Bering Sea

Acritarchs have received limited attention in palynological studies of the Cenozoic, although they have much potential both for refining Neogene and Quaternary stratigraphy, especially in mid- and high northern latitudes, and developing palaeoceanographical reconstructions. Here we formally describe and document the stratigraphical and palaeotemperature ranges (from foraminiferal Mg/Ca) of four new acritarch species: Cymatiosphaera? aegirii sp. nov., Cymatiosphaera? fensomei sp. nov., Cymatiosphaera? icenorum sp. nov. and Lavradosphaera canalis sp. nov. In reviewing the stratigraphical distributions of all species of the genus Lavradosphaera De Schepper & Head, 2008, we demonstrate their correlation potential between the North Atlantic and Bering Sea in the Pliocene. Additionally, Lavradosphaera lucifer De Schepper & Head, 2008 and Lavradosphaera canalis sp. nov., while not themselves overlapping stratigraphically, have morphological intermediates that do partially overlap and may represent an evolutionary trend consequent upon climate cooling in the Late Pliocene. Finally, we show that the highest abundances of the acritarchs presented here were living in the eastern North Atlantic, in surface-water temperatures not very different from today.

Age models, color measurements, and calculated sea surface temperatures of sediment cores from the Bering Sea and the Sea of Okhotsk

Past changes in North Pacific sea surface temperatures and sea-ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the North Atlantic. Here, we present new alkenone-based sea surface temperature records from the subarctic northwest Pacific and its marginal seas (Bering Sea and Sea of Okhotsk) for the time interval of the last 15 kyr, indicating millennial-scale sea surface temperature fluctuations similar to short-term deglacial climate oscillations known from Greenland ice-core records. Past changes in sea-ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the IP25 biomarker related to sea-ice diatoms. The deglacial variability in sea-ice extent matches the sea surface temperature fluctuations. These fluctuations suggest a linkage to deglacial variations in Atlantic meridional overturning circulation and a close atmospheric coupling between the North Pacific and North Atlantic. During the Holocene the subarctic North Pacific is marked by complex sea surface temperature trends, which do not support the hypothesis of a Holocene seesaw in temperature development between the North Atlantic and the North Pacific.

(Supplement T1) Clay mineral compositions at the Aleutian Basin of the Bering Sea from IODP sites 323-U1343

The clay mineral composition at IODP Exp. 323 Site U1343 in the Bering Sea was analyzed so as to unravel their provenance over glacial-interglacial cycles for the last 2.4 Ma. Smectite was negatively correlated with the sum of illite and chlorite; therefore, their ratio [S/(I + C)] was used as an indicator of clay mineral composition changes. In general, the S/(I + C) ratio was rather similar for glacial and interglacial periods during most of the last 2.4 Ma. In addition, these results overlap with those of surface sediments in the modern East Aleutian Basin, which suggests that smectite-rich clay particles are delivered from the Aleutians by the northward Bering Slope Current (BSC) rather than from rivers in western Alaska. However, some clay mineral compositions of the glacial periods after the Mid-Pleistocene Transition (MPT: 1.25-0.7 Ma) were characterized by low illite and relatively high smectite. During this period, extensive ice-rafting might have transported the smectite-rich clay particles to Site U1343 from the glacial shelf off Alaska and/or from glacial rivers from that area.

Stable carbon and nitrogen isotopic ratios of cores from the Bering Sea

Stable carbon and nitrogen isotopic ratios (d13C and d15N) of organic matter were measured in three sediment cores from deep basins of the Bering Sea to investigate past changes in surface nutrient conditions. For surface water reconstructions, hemipelagic layers in the cores were distinguished from turbidite layers (on the basis of their sedimentary structures and 14C ages) and analyzed for isotopic studies. Although d13C profiles may have been affected by diagenesis, both d15N and d13C values showed common positive anomalies during the last deglaciation. We explain these anomalies as reflecting suppressed vertical mixing and low nutrient concentrations in surface waters caused by injection of meltwater from alpine glaciers around the Bering Sea.

Synergistic effects of pCO2 and iron availability on nutrient consumption ratio of the Bering Sea phytoplankton community

Little is known concerning the effect of CO2 on phytoplankton ecophysiological processes under nutrient and trace element-limited conditions, because most CO2 manipulation experiments have been conducted under elements-replete conditions. To investigate the effects of CO2 and iron availability on phytoplankton ecophysiology, we conducted an experiment in September 2009 using a phytoplankton community in the iron limited, high-nutrient, low-chlorophyll (HNLC) region of the Bering Sea basin . Carbonate chemistry was controlled by the bubbling of the several levels of CO2 concentration (180, 380, 600, and 1000 ppm) controlled air, and two iron conditions were established, one with and one without the addition of inorganic iron. We demonstrated that in the iron-limited control conditions, the specific growth rate and the maximum photochemical quantum efficiency (Fv/Fm) of photosystem (PS) II decreased with increasing CO2 levels, suggesting a further decrease in iron bioavailability under the high-CO2 conditions. In addition, biogenic silica to particulate nitrogen and biogenic silica to particulate organic carbon ratios increased from 2.65 to 3.75 and 0.39 to 0.50, respectively, with an increase in the CO2 level in the iron-limited controls. By contrast, the specific growth rate, Fv/Fm values and elemental compositions in the iron-added treatments did not change in response to the CO2 variations, indicating that the addition of iron canceled out the effect of the modulation of iron bioavailability due to the change in carbonate chemistry. Our results suggest that high-CO2 conditions can alter the biogeochemical cycling of nutrients through decreasing iron bioavailability in the iron-limited HNLC regions in the future.

Coccoliths in phytoplankton of the Eastern Bering Sea in August 2001

Based on results of field observations in August 1998, July 2000, and August 2001 composition and quantitative distribution of coccolithophorids in the middle part of the Eastern Bering Sea shelf between 56°052'N and 59°019'N was characterized. Emiliania huxleyi abundance, biomass, and population structure as well as role of species in the coccolithophorid community and phytoplankton as a whole were evaluated. Abundance of the species in the upper mixed layer in bloom areas was 1-3 mln cells/l and biomass made up 30-75 mg C/m**3. E. huxleyi share in total phytoplankton numbers and biomass at that reached 98% and 84% respectively. Significant spatial heterogeneity of E. huxleyi, quantitative distribution and population size structure, as well as asynchronism in population development in neighboring parts of the bloom area were shown. The time period, during which population structure in certain part of the area shifts from domination of juvenile cells without coccoliths to a phase of active detritus formation with dying coccolithophorid cells involved, may be estimated as two weeks. A conclusion is made that after anomalous E. huxleyi bloom in 1997 mass development of coccolithophorids became a characteristic feature of phytoplankton community's seasonal succession in the middle part of the Eastern Bering Sea shelf.